Support for Fischer-Tropsch catalyst having improved activity

ABSTRACT

A process is disclosed for preparing a Fischer-Tropsch catalyst precursor and a catalyst made from the precursor. The process includes contacting an alumina catalyst support material with a first solution containing a vanadium compound and a phosphorus compound, to obtain a modified catalyst support material. The modified catalyst support material is calcined at a temperature of at least 500° C. The calcined modified catalyst support has a pore volume of at least 0.4 cc/g. The modified catalyst support is less soluble in acid solutions than an equivalent unmodified catalyst support. The modified catalyst support is contacted with a second solution which includes a precursor compound of an active cobalt catalyst component and glutaric acid to obtain a catalyst precursor. The catalyst precursor is reduced to activate the catalyst precursor to obtain the Fischer-Tropsch catalyst. The catalyst has enhanced hydrothermal stability and good activity.

FIELD

The present disclosure relates generally to catalysts for use inFischer-Tropsch processes in which synthesis gas is converted tohydrocarbon products.

BACKGROUND

Supported cobalt catalysts are commonly used in the Fischer-Tropschsynthesis (FTS) step in gas-to-liquid (GTL) processes due to their highactivity and selectivity to heavy hydrocarbons. The performance of thecobalt catalysts is very important for the economics of the GTL process.The FTS process is typically performed in a three-phase slurry reactor.An important advantage of the slurry reactor over fixed bed reactors isthe greatly improved heat removal capability and ease of temperaturecontrol.

Alumina is one of the most desirable catalyst supports. Due to its highsurface area and good mechanical properties, the gamma form of aluminahas been used widely in industry for many catalytic applications.However, in an acidic or alcohol containing reaction medium such asFischer-Tropsch synthesis conditions to produce wax, or other reactionsproceeding in aqueous medium such as alcohol, ether, and estersyntheses, an alumina support exhibits a stability problem. Alumina maydissolve or leach slowly in the reactor due to attacks of acid andalcohol byproducts in the reaction medium. Dissolution of aluminasupport in acid medium is detrimental in catalyst stability. Thedissolution of the support may cause poor catalyst integrity andpossible fines generation. Fines generation will hurt the subsequentfiltration and post processing operations. High metal or metal compoundcontent in a Fischer-Tropsch product is undesirable because suchcontaminants could have adverse effects for the Fischer-Tropsch process,such as causing reactor plugging or significantly reducing catalystlife. As a result, it is important that the product of theFischer-Tropsch process be free of metal and other contaminants thatcould adversely affect its subsequent processing. Thus it is highlydesirable to have an alumina catalyst support with much improved acidresistance.

The churning of the contents of the three-phase slurry reactor exerts asignificant mechanical stress on the suspended catalysts, placing a highpremium on their mechanical integrity to avoid attrition of the catalystparticles in the slurry. By attrition is meant physical breakdown of thecatalyst particles caused by friction or grinding as a result of impactwith other particles. The cobalt catalyst in the FTS slurry isadditionally susceptible to hydrothermal attack that is inherent to theFTS process at conventional slurry conditions because of the presence ofwater at high temperatures. Such hydrothermal attack is particularly afactor on exposed and unprotected catalyst support material, resultingin weaker support material such that the catalyst is more susceptible toattrition. Such catalyst attrition can result in contamination of theproduced heavy hydrocarbons (i.e., wax) with fines. It would bedesirable to have a cobalt Fischer-Tropsch catalyst having improvedhydrothermal stability for use in slurry reactors. It would further bedesirable to have a cobalt Fischer-Tropsch catalyst having improvedcatalytic activity.

SUMMARY

In one aspect, a process is provided for preparing a Fischer Tropschcatalyst precursor. The process includes contacting an alumina catalystsupport material with a first solution containing a vanadium compoundand a phosphorus compound. The catalyst support material is calcined ata temperature of at least 500° C. to obtain a modified catalyst supporthaving a pore volume of at least 0.4 cc/g. The modified catalyst supportloses no more than 8% of its pore volume when exposed to water vapor.The modified catalyst support is contacted with a second solution whichincludes a precursor compound of an active cobalt catalyst component andan organic compound to obtain a catalyst precursor. In one embodiment,the organic compound is glutaric acid.

In another aspect, a process is provided for preparing a Fischer Tropschcatalyst. The catalyst precursor is prepared as described above, and thecatalyst precursor is reduced to activate the catalyst precursor toobtain the Fischer Tropsch catalyst.

In another aspect, a process is provided for Fischer Tropsch synthesisincluding contacting a gaseous mixture comprising carbon monoxide andhydrogen with the Fischer Tropsch catalyst prepared as described aboveat a pressure of from 0.1 to 3 MPa and a temperature of from 180 to 260°C. A product comprising C₅₊ hydrocarbons is produced.

DESCRIPTION OF THE DRAWINGS

These and other objects, features and advantages of the presentinvention will become better understood with reference to the followingdescription, appended claims and accompanying drawings where:

FIG. 1 is a graph illustrating the dissolution profile ofvanadium-phosphorus modified alumina supports according to one exemplaryembodiment.

FIG. 2 is a graph of x-ray diffraction (XRD) results before and aftersteaming comparing one exemplary embodiment modified with glutaric acidwith comparative examples.

FIG. 3 is a graph of volume distribution function, also referred to asvolume weighted distribution profile, versus particle size for cobaltoxide crystallite size for comparative and exemplary catalysts.

DETAILED DESCRIPTION

In one embodiment, a catalyst support is modified with a first solutioncontaining a vanadium compound and a phosphorus compound, in order tominimize the undesirable effects of hydrothermal attack on an FTScatalysts based on the support. The use of the modified catalyst supportcan reduce the occurrence of ultra-fine particles contaminating the waxyhydrocarbon product of the FTS step in a GTL process. The modifiedcatalyst support, also referred to herein as a Fischer-Tropsch catalystprecursor, is prepared according to the following process. Aluminaparticles are selected as the catalyst support material. In oneembodiment, gamma alumina particles are selected as the catalyst supportmaterial. Alternatively, boehmite particles can be used as the startingcatalyst support material.

In one embodiment, the gamma alumina particles have a diameter from 10μm to 200 μm. The average particle size may be from 60 μm to 100 μm. Inone embodiment, the gamma alumina particles have a BET pore volume offrom 0.4 cc/g to 1.0 cc/g.

Vanadium and phosphorous are added to alumina by co-impregnation withdifferent V/P molar ratios. In one embodiment, ammonium metavanadate andphosphoric acid are dissolved in water. The solution can be heated tofacilitate dissolution. The solution can then be added to the aluminacatalyst support material by any suitable method, e.g., incipientwetness impregnation method. In one embodiment, the molar ratio ofvanadium to phosphorus in the solution is from 0.05 to 6.0, and evenfrom 0.1 to 4.0. The combined amount of vanadium and phosphorus in thefirst solution can be from 1 to 10 weight percent. The modified catalystsupport material can then be slowly dried, e.g., at a temperature offrom 110° to 120° C. to spread the metals over the entire support. Thedrying step can be conducted in air.

The modified catalyst support material is then calcined in flowing airat a temperature of at least 500° C. to obtain a modified catalystsupport. In one embodiment, the catalyst support material is calcined ata temperature of at least 700° C. Calcination should be conducted byusing a slow heating rate of, for example, 0.5° to 3° C. per minute orfrom 0.5° to 1° C. per minute, and the catalyst should be held at themaximum temperature for a period of between 1 and 20 hours.

The modified catalyst support has been found to have a pore volume of atleast 0.4 cc/g. The test for hydrothermal stability of the catalystsupport is performed using a steaming test. The steaming test includesexposing 1-2 g of modified catalyst support to about 15-30 g of waterfor 2-20 hours in an autoclave at a temperature of 220-240° C. Themodified catalyst support sample is cooled down to room temperature andthen dried at 120° C. for 2 hours. Physical analyses are carried out onthe modified support alumina support before and after the steamtreatment. The modified catalyst support has been found to lose no morethan 8% of its pore volume when exposed to water vapor.

The modified catalyst support is then contacted with a second solutionthat contains a precursor compound of an active cobalt catalystcomponent and an organic compound to obtain a FTS catalyst precursor. Inone embodiment, the modified catalyst support is contacted with thesecond solution by impregnation, e.g., incipient wetness impregnation.The organic compound can be a carboxylic acid containing five carbonatoms. Preferably, the organic compound is glutaric acid. The amount ofglutaric acid in the second solution can be from 2 to 15 μmol glutaricacid/m² relative to the modified support surface area.

The impregnated catalyst is then dried. The impregnation using thesecond solution can be repeated as needed until the desired cobaltloading is achieved. Multiple impregnations are often needed to achievethe desired metal loading, with intervening drying and calcinationtreatments to disperse and decompose the metal salts. The secondsolution and support are stirred while evaporating the solvent at atemperature of from about 25° to about 50° C. until “dryness.” Theimpregnated catalyst is slowly dried at a temperature of from about 110°to about 120° C. for a period of about 1 hour so as to spread the metalsover the entire support. The drying step may be conducted at a very slowrate in air.

The dried catalyst may then be reduced or it may be calcined first. Thedried catalyst is calcined by heating slowly in flowing air, for example10 cc/gram/minute, to a temperature in the range of from about 200° toabout 350° C., for example, from about 250° to about 300° C., that issufficient to decompose the metal salts and fix the metals. Theaforesaid drying and calcination steps can be done separately or can becombined. However, calcination should be conducted by using a slowheating rate of, for example, 0.5° to about 3° C. per minute or fromabout 0.5° to about 1° C. per minute and the catalyst should be held atthe maximum temperature for a period of about 1 to about 20 hours, forexample, for about 2 hours.

The foregoing impregnation steps are repeated with additional solutionsin order to obtain the desired metal loading, i.e., from 5 wt % to 45 wt% cobalt, even from 20 wt % to 35 wt % cobalt. Metal promoters can beadded with the FT component, but they may be added in other impregnationsteps, separately or in combination, before, after or betweenimpregnations of FT component. In one embodiment, the catalyst precursorfurther contains a promoter selected from the group consisting ofplatinum, ruthenium, silver, palladium, lanthanum, cerium andcombinations thereof. The promoter can be added to the second solutionor to a subsequent solution, and applied to the modified catalystsupport by impregnation. The catalyst precursor can contain the promoterin an amount from 0.01 wt % to 5 wt %.

A Fischer-Tropsch catalyst can then be prepared from the catalystprecursor by reducing the catalyst precursor to activate the catalystprecursor. In one embodiment, the catalyst precursor is placed in a tubereactor in a muffle furnace. The tube can be purged first with nitrogengas at ambient temperature, after which time the gas feed can be changedto pure hydrogen. The temperature to the reactor can be increased, forexample, to 450° C. at a rate of 1° C./minute and then held at thattemperature for ten hours. After this time, the gas feed can be switchedto nitrogen to purge the system and the unit can be cooled to ambienttemperature. Then a gas mixture of 1 volume % O₂/N₂ can be passed upthrough the catalyst bed at 750 sccm for 10 hours to passivate thecatalyst.

Advantageously, the Fischer-Tropsch catalyst prepared as describedherein loses no more than about 10%, even no more than 8%, of its porevolume when exposed to water vapor. In one embodiment, the catalystloses not more than 6% its pore volume when the catalyst is contactedwith a feed stream at a temperature greater than 200° C. in the presenceof water. Furthermore, the Fischer-Tropsch catalyst prepared asdescribed herein wherein the second solution contains glutaric acid hasbeen found to have cobalt oxide (Co₃O₄) crystallites having an averagesize of no greater than 20 nm, even from 6 to 20 nm. Such smallcrystallite size results in high catalytic activity.

In one embodiment, a process of Fischer-Tropsch synthesis is conductedby contacting a gaseous mixture comprising carbon monoxide and hydrogenwith the Fischer-Tropsch catalyst prepared as disclosed herein at apressure of from 0.1 to 3 MPa and a temperature of from 180 to 260° C.The FTS process can occur in a slurry reactor or a continuously stirredtank reactor. The resulting product contains C₅₊ hydrocarbons.

EXAMPLES Test Methods

Average Crystallite Particle Size by X-Ray Diffraction (XRD)

Cobalt oxide (Co₃O₄) crystallite size was estimated using the Scherrerequation with Warren's correction. Particle sizes by Scherrer equationwere calculated for Co₃O₄ at the 311 reflection with 2Θ of about 36.8°.

Cobalt oxide (Co₃O₄) crystallite size was also estimated using the XRDDouble Voigt method, using the procedure given below for calculatingcrystallite size distributions.

Crystallite Size Distribution

Crystallite size distributions were calculated from peak profilesevaluated with a Voigt function, which is a convolution of Lorentzianand Gaussian functions. The resulting Lorentzian and Gaussian integralbreadths were used as inputs to the computer program BREADTH (J. Appl.Cryst. 26 (1993) 97-103). The program calculates the volume weighteddistribution profiles using the Double Voigt method and the volumeweighted average particle size.

Full Width at Half the Maximum (FWHM)

Full Width at Half the Maximum (FWHM) is a parameter used to indicatethe broadness of a peak, in this case the volume distribution function.

The values of FWHM in Table 2 were calculated by modeling particle sizedistributions, in FIG. 3, with an asym2sig function in OriginPro dataanalysis software (available from OriginLab Corporation, Northampton,Mass.) with the form:

$y = {y_{0} + {A \cdot \frac{1}{1 + e^{- \frac{x - x_{c} + {w_{1}/2}}{w_{2}}}} \cdot \left\lbrack {1 - \frac{1}{1 + e^{- \frac{x - x_{c} + {w_{1}/2}}{w_{3}}}}} \right\rbrack}}$where w₁ is the FWHM, y₀ is the offset, x_(c) is the center, A is theamplitude, w₂ is low-side variance, and w₃ is the high-side variance.

Comparative Example 1

Gamma alumina SA63158 (obtained from Saint-Gobain NorPro Corporation,Stow, Ohio) was used as a catalyst support.

Example 1

Vanadium and phosphorous were supported on the gamma alumina byimpregnation with vanadium and phosphorous having a molar ratio of 1.2.NH₄VO₃ (obtained from Sigma-Aldrich, St. Louis, Mo.) was added todistilled water and then phosphoric acid was added to the vanadiumsolution. This solution was stirred for 1 h at 70° C. The solution wasthen cooled to room temperature and added to the gamma alumina supportsby incipient wetness impregnation method. The material was then dried inan oven at 120° C. overnight. Finally, the dried modified aluminasupport was calcined at 750° C. for 2 hours in a muffle furnace.

Comparative Example 1A

PB600 boehmite alumina support (obtained from obtained from PacificIndustrial Development Coporation) was dispersed in deionized water toachieve a solid content of about 20% by weight of the solution. Theslurry was subsequently spray dried to form spherical granules. Thespray dried material was then further treated in an oven at 120° C.overnight. Finally, the dried alumina support was calcined at 750° C.for 2 hours in a muffle furnace.

Example 1A

PB600 boehmite alumina support (obtained from obtained from PacificIndustrial Development Coporation) was dispersed in deionized water toachieve a solid content of about 25% by weight of the solution. NH₄VO₃(obtained from Sigma-Aldrich, St. Louis, Mo.) and phosphoric acid(obtained from Sigma-Aldrich, St. Louis, Mo.) were dissolved indeionized water. This solution was stirred for 1 h at 70° C. Thesolution was then cooled to room temperature and added to the aboveboehmite slurry. The slurry was subsequently spray dried to formspherical granules. The spray dried material was then further treated inan oven at 120° C. overnight. Finally, the dried modified aluminasupport was calcined at 750° C. for 2 hours in a muffle furnace.

Comparative Example 1B

85% of 18N480 boehmite (obtained from Sasol, which had a bulk density0.87 g/ml) and 15% of Pural TH100 (obtained from Sasol, which had a bulkdensity 0.39 g/ml) were dispersed in deionized water to achieve a solidcontent of about 20% by weight of the solution. The slurry wassubsequently spray dried to form spherical granules. The spray driedmaterial was then further treated in an oven at 120° C. overnight.Finally, the dried alumina support was calcined at 750° C. for 2 hoursin a muffle furnace.

Example 1B

85% of 18N480 boehmite (obtained from Sasol, which had a bulk density0.87 g/ml) and 15% of Pural TH100 (obtained from Sasol, which had a bulkdensity 0.39 g/ml) were dispersed in deionized water to achieve a solidcontent of about 20% by weight of the solution. NH₄VO₃ (obtained fromSigma-Aldrich, St. Louis, Mo.) and phosphoric acid (obtained fromSigma-Aldrich, St. Louis, Mo.) were dissolved in deionized water. Thissolution was stirred for 1 h at 70° C. The solution was then cooled toroom temperature and added to the above boehmite slurry. The slurry wassubsequently spray dried to form spherical granules. The spray driedmaterial was then further treated in an oven at 120° C. overnight.Finally, the dried modified alumina support was calcined at 750° C. for2 hours in a muffle furnace.

Comparative Example 1C

85% of 18N480 boehmite (obtained from Sasol, which had a bulk density0.87 g/ml) and 15% of Pural TH100 (obtained from Sasol, which had a bulkdensity 0.39 g/ml) were dispersed in deionized water to achieve a solidcontent of about 20% by weight of the solution. The slurry wassubsequently spray dried to form spherical granules. The spray driedmaterial was then further treated in an oven at 120° C. overnight.Finally, the dried alumina support was calcined at 750° C. for 2 hoursin a muffle furnace

Example 1C

Vanadium and phosphorous were supported on the alumina by impregnationwith vanadium and phosphorous having a molar ratio of 1.2. NH4VO3(obtained from Sigma-Aldrich, St. Louis, Mo.) was added to distilledwater; and then phosphoric acid was added to the vanadium solution. Thissolution was stirred for 1 h at 70° C. The solution was then cooled toroom temperature and added to the alumina support used in ComparativeExample 1C by incipient wetness impregnation method. The material wasthen dried in an oven at 120° C. overnight. Finally, the dried modifiedalumina support was calcined at 750° C. for 2 hours in a muffle furnace.

Acid Resistance of Supports

When alumina dissolves in an aqueous acid medium, aluminum ions areformed. A method to obtain the cumulative aluminum ion dissolutionprofile was disclosed U.S. Pat. No. 6,875,720 to Van Berge et al., inwhich the concentration of aluminum ions was estimated usingconductivity measurements at a constant pH as a function of time.

In the present disclosure, the increase of aluminum ions over time wasobserved by monitoring the conductivity over time using a proceduresimilar to that disclosed by van Berge et al. For this experiment, 2 gof a support sample was slurried in a dilute nitric acid solution. Thenthe conductivity was monitored for 30-40 hours. The increase of aluminumions over time can be monitored by measuring the conductivity of thesolution using Metrohm Conductivity Cell with Pt 1000 (C=0.7) over arange of 5-20,000 μS/cm at a constant pH of 2.0 using Metrohm Gelelectrode with NTC (using plug head U). The pH was kept constant at pH2.0 by the automated addition of a 10% nitric acid solution using the907 Titrando by Metrohm USA (Riverview, Fla.) and Tiamo™ titrationsoftware available from Metrohm USA. The conductivity change is due toaluminum dissolution to form Al³⁺. The conductivity change in μS/cm isplotted as a function of time in seconds in FIG. 1. The FIG. 100 clearlyindicates that vanadium-phosphorus modified alumina (Example 1, shown ascurve 104) shows much lower conductivity increase than pure gammaalumina at constant acid consumption (Comparative Example 1, shown ascurve 102), demonstrating the present modified alumina exhibits improvedacid resistance.

Hydrothermal Stability of Alumina Supports

Hydrothermal stability testing of the modified support of Example 1 andthe unmodified support of Comparative Example 1 was performed in a highpressure Parr reactor. 2 grams of support sample and 15 g of water werecharged to an autoclave and heated at 220° C. and a pressure of 370 psigfor 2 hours. The support sample was cooled down to room temperature andthen dried at 120° C. for 2 hours. Two samples (before and aftersteaming) were then analyzed for change in pore volume. Pore volume ofsupport samples were determined from nitrogen adsorption/desorptionisotherms measured at −196° C. using a Tristar analyzer available fromMicromeritics Instrument Corporation (Norcross, Ga.). Prior to gasadsorption measurements, the catalyst samples were degassed at 190° C.for 4 hours. Table 1 shows the relative percentage change in pore volumeof the modified support of Example 1 and the un-modified support ofComparative Example 1, as calculated by the following formula:% change=(pore volume before steam test-pore volume after steamtest)/(pore volume before steam test)

From Table 1 it is evident that the vanadium-phosphorus modifiedsupports showed enhanced hydrothermal stability compared to theunmodified alumina support. The catalysts using the modified supportslost no more than 6% of their pore volume when exposed to water vapor.

TABLE 1 Pore Volume, cc/g Before After % Example Number steamingsteaming Change Comparative 0.574 0.110 80.8 Example 1 Example 1 0.5070.481 5.1 Comparative 0.3979 0.0385 90.3 Example 1A Example 1A 0.34910.3394 2.77 Comparative 0.4642 0.2041 56.03 Example 1B Example 1B 0.45010.4230 7.86 Comparative 0.4642 0.2041 56.03 Example 1C Example 1C 0.40520.3867 4.56

X-ray diffraction (XRD) results of the supports before and aftersteaming are shown in FIG. 2 (200). The comparative XRD results in FIG.2 show that the unmodified gamma alumina was completely transformed toboehmite after the steam treatment (Comparative Example 1, shown ascurve 202 before steam treatment and as 204 after steam treatment).However, the XRD pattern of the vanadium-phosphorus modified alumina(Example 1, shown as curve 206) after the same steam treatment shows agamma alumina pattern.

Comparative Example 2

A three-step incipient wetness impregnation method was used to prepare aFischer-Tropsch catalyst. A solution was prepared by dissolvingcobalt(II) nitrate hexahydrate (obtained from Sigma-Aldrich),tetraammineplatinum(II) nitrate (obtained from Alfa Aesar, Ward Hill,Mass.) and lanthanum (III) nitrate hexahydrate (obtained fromSigma-Aldrich) in water. Alumina from Comparative Example 1 wasimpregnated by using one-third of this solution to achieve incipientwetness. The prepared catalyst was then dried in air at 120° C. for 16hours in a box furnace and was subsequently calcined in air by raisingits temperature at a heating rate of 1° C./min to 300° C. and holding itat that temperature for 2 hours before cooling it back to ambienttemperature. The above procedure was repeated to obtain the followingloading of Co, Pt and La₂O₃ on the support: 30 wt % Co, 0.05 wt % Pt, 1wt % La₂O₃ and 68.95 wt % alumina.

Comparative Example 3

A three-step incipient wetness impregnation method was used to preparethe Fischer-Tropsch catalyst. A solution was prepared by dissolvingcobalt(II) nitrate hexahydrate (obtained from Sigma-Aldrich),tetraammineplatinum (II) nitrate (obtained from Alfa Aesar) andlanthanum (III) nitrate hexahydrate (obtained from Sigma-Aldrich) inwater. Modified alumina from Example 1 was impregnated by usingone-third of this solution to achieve incipient wetness. The preparedcatalyst was then dried in air at 120° C. for 16 hours in a box furnaceand was subsequently calcined in air by raising its temperature at aheating rate of 1° C./min to 300° C. and holding it at that temperaturefor 2 hours before cooling it back to ambient temperature. The aboveprocedure was repeated to obtain the following loading of Co, Pt andLa₂O₃ on the support: 30 wt % Co, 0.05% Pt and 1 wt % La₂O₃ and 68.95 wt% alumina.

Comparative Example 4

A three-step incipient wetness impregnation method was used to preparethe Fischer-Tropsch catalyst. A solution was prepared by dissolvingcobalt(II) nitrate hexahydrate (obtained from Sigma-Aldrich),tetraammineplatinum (II) nitrate (obtained from Alfa Aesar) andlanthanum (III) nitrate hexahydrate (obtained from Sigma-Aldrich) and aspecified amount of citric acid (obtained from Sigma-Aldrich) asidentified in Table 2, in water. Modified alumina from Example 1 wasimpregnated by using one-third of this solution to achieve incipientwetness. The prepared catalyst was then dried in air at 120° C. for 16hours in a box furnace and was subsequently calcined in air by raisingits temperature at a heating rate of 1° C./min to 300° C. and holding itat that temperature for 2 hours before cooling it back to ambienttemperature. The above procedure was repeated to obtain the followingloading of Co, Pt and La₂O₃ on the support: 30 wt % Co, 0.05% Pt and 1wt % La₂O₃ and 68.95 wt % alumina.

Comparative Example 5

A three-step incipient wetness impregnation method was used to preparethe Fischer-Tropsch catalyst. A solution was prepared by dissolvingcobalt(II) nitrate hexahydrate (obtained from Sigma-Aldrich),tetraammineplatinum (II) nitrate (obtained from Alfa Aesar) andlanthanum (III) nitrate hexahydrate (obtained from Sigma-Aldrich) and aspecified amount of aconitic acid (obtained from Sigma-Aldrich) asidentified in Table 2, in water. Modified alumina from Example 1 wasimpregnated by using one-third of this solution to achieve incipientwetness. The prepared catalyst was then dried in air at 120° C. for 16hours in a box furnace and was subsequently calcined in air by raisingits temperature at a heating rate of 1° C./min to 300° C. and holding itat that temperature for 2 hours before cooling it back to ambienttemperature. The above procedure was repeated to obtain the followingloading of Co, Pt and La₂O₃ on the support: 30 wt % Co, 0.05% Pt and 1wt % La₂O₃ and 68.95 wt % alumina.

Examples 2-8

A three-step incipient wetness impregnation method was used to preparethe Fischer-Tropsch catalysts. A solution was prepared by dissolvingcobalt(II) nitrate hexahydrate (obtained from Sigma-Aldrich),tetraammineplatinum (II) nitrate (obtained from Alfa Aesar) andlanthanum (III) nitrate hexahydrate (obtained from Sigma-Aldrich) and aspecified amount of glutaric acid (obtained from Sigma-Aldrich) asidentified in Table 2, in water. Modified alumina supports from Example1 were impregnated by using one-third of this solution to achieveincipient wetness. The prepared catalysts were then dried in air at 120°C. for 16 hours in a box furnace and subsequently calcined in air byraising their temperature at a heating rate of 1° C./min to 300° C. andholding at that temperature for 2 hours before cooling back to ambienttemperature. The above procedure was repeated to obtain the followingloading of Co, Pt and La₂O₃ on the supports: 30 wt % Co, 0.05% Pt and 1wt % La₂O₃ and 68.95 wt % alumina.

Example 9

A three-step incipient wetness impregnation method was used to preparethe Fischer-Tropsch catalyst. A solution was prepared by dissolvingcobalt(II) nitrate hexahydrate (obtained from Sigma-Aldrich),tetraammineplatinum (II) nitrate (obtained from Alfa Aesar) andlanthanum (III) nitrate hexahydrate (obtained from Sigma-Aldrich) and aspecified amount of glutaric acid (obtained from Sigma-Aldrich) asidentified in Table 2, in water. Modified alumina supports from Example1C were impregnated by using one-third of this solution to achieveincipient wetness. The prepared catalyst was then dried in air at 120°C. for 16 hours in a box furnace and subsequently calcined in air byraising their temperature at a heating rate of 1° C./min to 300° C. andholding at that temperature for 2 hours before cooling back to ambienttemperature. The above procedure was repeated to obtain the followingloading of Co, Pt and La₂O₃ on the supports: 25 wt % Co, 0.04% Pt and 1wt % La₂O₃ and 73.96 wt % alumina.

Catalysts were analyzed for their average crystallite size using XRD,both by XRD Scherrer method and XRD Double Voigt method. The two XRDmethods gave comparable average sizes. As seen from the data in Table 2,the use of glutaric acid reduces the average Co₃O₄ crystallite size. Theaverage Co₃O₄ crystallite size is shown to decrease as the amount ofglutaric acid used increases.

In FIG. 3 (300), the volume distribution function is plotted against thecrystallite size in angstroms. As the figure shows, the examples of theinvention, i.e., Examples 3 (shown as curve 306), 5 (shown as curve 308)and 7 (shown as curve 302) that were prepared using glutaric acid havenarrower crystallite size distributions than the comparative examples.Comparative Examples 3, 4 and 5 are shown as curves 304, 310 and 312,respectively. This can be further seen from the FWHM data in Table 2,indicating that the broadness of the distribution of the Co₃O₄crystallite size is desirably narrowed as the amount of glutaric acidused increases.

Thus it is shown that an advantage of the disclosed method is theability to prepare catalysts having narrower particle size distribution,to avoid synthesizing cobalt particles of undesirable size. Thedisclosed method can be used to avoid making particles that areundesirably small, which may form methane and have high deactivation, aswell as to avoid making particles that are undesirably large, which maybe less active.

TABLE 2 μmol acid/m² Weight Average Co₃O₄ Average Co₃O₄ Full Width atHalf surface area of acid, size, nm, by size, nm, by XRD the Maximum ofmodified g/60 g XRD Scherrer Double Voigt (FWHM), Example Acid supportsupport method method angstroms Comparative No acid No acid 0 23 27 296Example 3 Comparative Citric acid 8.07 13.1 25 26 255 Example 4Comparative Aconitic acid 8.09 11.9 27 24 234 Example 5 Example 2Glutaric acid 2.69 3 20 Not available Not available Example 3 Glutaricacid 3.58 4 17 15 151 Example 4 Glutaric acid 4.48 5 15 Not availableNot available Example 5 Glutaric acid 5.38 6 12 11 118 Example 6Glutaric acid 8.06 9 12 Not available Not available Example 7 Glutaricacid 10.75 12 10 10  92 Example 8 Glutaric acid 13.44 15 10 Notavailable Not available Example 9 Glutaric acid 8.06 9 12 13 121

Hydrothermal Stability of Fischer-Tropsch Catalysts

The hydrothermal stability of the modified and unmodified catalysts wasperformed in a high pressure Parr reactor. 2 grams of catalyst samplesand 30 g of water were charged to an autoclave and heated at 220° C. anda pressure of 390 psig for 20 hours. The catalyst samples were cooled toroom temperature and then dried at 120° C. for 2 hours. Each catalystsample was tested for change in pore volume, before and after steamingPore volume of catalyst samples were determined from nitrogenadsorption/desorption isotherms measured at −196° C. using a Tristaranalyzer available from Micromeritics Instrument Corporation (Norcross,Ga.). Prior to gas adsorption measurements, the catalyst samples weredegassed at 190° C. for 4 hours.

Table 3 shows the relative percentage change in pore volume of thecatalyst samples, as calculated by the following formula:% change=(pore volume before steam test-pore volume after steamtest)/(pore volume before steam test)

TABLE 3 Pore Volume, cc/g Fresh Catalyst after % Example Number catalyststeaming Change Comparative 0.2348 0.1598 31.9 Example 2 Comparative0.2333 0.2195 5.9 Example 3 Example 2 0.2248 0.2089 7.1 Example 3 0.21960.2124 3.3 Example 4 0.2258 0.2155 4.6 Example 5 0.2260 0.2114 6.4Example 6 0.2269 0.2140 5.7 Example 7 0.2317 0.2215 4.4 Example 8 0.24060.2274 5.5 Example 9 0.2049 0.2013 1.8

It can be seen from Table 3 that the performance of the catalyst on thevanadium-phosphorus modified supports showed enhanced hydrothermalstability compared to the catalyst on the unmodified alumina supportwith same cobalt loading.

Catalyst Activation

Twenty grams of each catalyst prepared as described above was charged toa glass tube reactor. The reactor was placed in a muffle furnace withupward gas flow. The tube was purged first with nitrogen gas at ambienttemperature, after which time the gas feed was changed to pure hydrogenwith a flow rate of 750 sccm. The temperature to the reactor wasincreased to 350° C. at a rate of 1° C./minute and then held at thattemperature for ten hours. After this time, the gas feed was switched tonitrogen to purge the system and the unit was then cooled to ambienttemperature. Then a gas mixture of 1 volume % O₂/N₂ was passed upthrough the catalyst bed at 750 sccm for 10 hours to passivate thecatalyst. No heating was applied, but the oxygen chemisorption andpartial oxidation exotherm caused a momentary temperature rise. After 10hours, the gas feed was changed to pure air, the flow rate was loweredto 200 sccm and then kept for two hours. Finally, the catalyst wasdischarged from the glass tube reactor.

A 1 liter CSTR was used for the slurry FTS reaction. The catalyst wastransferred to the CSTR unit to mix with 300 g of C-80 Sasol wax. Thecatalyst was flushed with nitrogen for a period of two hours, afterwhich time the gas feed was switched to pure hydrogen at a flow rate of500 sccm. The temperature was slowly raised to 120° C. at a temperatureinterval of 1° C./minute, held there for a period of one hour, thenraised to 250° C. at a temperature interval of 1° C./minute and held atthat temperature for 10 hours. After this time, the catalyst was cooledto 180° C. while remaining under a flow of pure hydrogen gas.

Fischer-Tropsch Activity

Catalysts prepared and activated as described above were each subjectedto a synthesis run in which the catalyst was contacted with syngascontaining hydrogen and carbon monoxide. Experimental conditions andresults are given in Table 4.

TABLE 4 Comparative Comparative Run Conditions Example 2 Example 3Temperature, ° C. 227 227 Pressure, psig 326 326 Space Velocity, cc/g/h5000 5000 H₂/CO ratio 1.6 1.6 Results CO Conversion, (mol %) 50.9 49.7C₅₊ Productivity, g/g/h 0.401 0.403 Selectivity, mol % CH₄ 5.1 4.2 C₂0.8 0.7 C₃ 2.5 2.3 C₄ 2.8 2.5 C₅+ 87.0 88.3 CO₂ 1.8 2.0

It can be seen from Table 4 that the performance of the catalyst on thevanadium-phosphorus modified support did not affect the FT performanceof the catalyst on the unmodified alumina with same cobalt loading.

As shown Table 5, the catalysts prepared using an impregnation with asecond solution containing glutaric acid having a lower average Co₃O₄crystallite size show a higher level of catalytic activity.

TABLE 5 Run Conditions Comparative Example 3 Example 5 Example 7Temperature, ° C. 227 227 227 227 227 227 227 227 227 227 Pressure, psig326 326 326 326 326 326 326 326 326 326 Space Velocity, 6500 5000 40009000 8000 9000 8000 6500 5000 4000 cc/g/h H₂/CO ratio 1.6 1.6 1.6 1.61.6 1.6 1.6 1.6 1.6 1.6 Results CO Conversion, 48.6 49.7 44.1 48.5 49.348.2 48.5 50.6 53.2 559 (mol %) C₅+ Productivity, 0.520 0.403 0.2780.720 0.647 0.726 0.644 0.542 0.432 0.354 g/g/h Selectivity, mol % CH₄4.1 4.2 5.0 4.2 4.0 3.7 3.8 3.6 3.5 3.4 C₂ 0.6 0.7 0.9 0.5 0.6 0.4 0.50.5 0.6 0.5 C₃ 2.1 2.3 2.9 1.9 1.9 1.6 1.7 1.8 1.9 2.0 C₄ 2.3 2.5 3.12.4 2.4 2.0 2.2 2.2 2.3 2.4 C₅+ 89.5 88.3 85.6 89.8 89.3 91.1 90.3 89.788.3 86.3 CO₂ 1.3 2.0 2.4 1.2 1.7 1.1 1.4 2.1 3.4 5.3

Unless otherwise specified, the recitation of a genus of elements,materials or other components, from which an individual component ormixture of components can be selected, is intended to include allpossible sub-generic combinations of the listed components and mixturesthereof. Also, “comprise,” “include” and its variants, are intended tobe non-limiting, such that recitation of items in a list is not to theexclusion of other like items that may also be useful in the materials,compositions, methods and systems of this invention.

From the above description, those skilled in the art will perceiveimprovements, changes and modifications, which are intended to becovered by the appended claims.

What is claimed is:
 1. A process for preparing a Fischer Tropschcatalyst precursor, the process comprising: a. impregnating an aluminacatalyst support material with a first solution comprising ammoniummetavanadate and phosphoric acid, to obtain a catalyst support material;b. calcining the treated catalyst support material at a temperature ofat least 500° C. to obtain a modified catalyst support having a modifiedsupport surface area and a pore volume of at least 0.4 cc/g; wherein themodified catalyst support loses no more than 8% of said support's porevolume when exposed to water vapor; and c. contacting the modifiedcatalyst support with a second solution comprising a precursor compoundof an active cobalt catalyst component and glutaric acid to obtain acatalyst precursor.
 2. The process of claim 1, wherein the aluminacatalyst support material comprises gamma alumina.
 3. The process ofclaim 1, wherein the alumina catalyst support material comprisesboehmite.
 4. The process of claim 1, wherein the calcining of thetreated catalyst support material occurs at a temperature of at least700° C.
 5. The process of claim 1, wherein the first solution comprisesfrom 1 to 10 weight percent of vanadium and phosphorus.
 6. The processof claim 1, wherein the first solution comprises vanadium and phosphorusat a molar ratio of vanadium to phosphorus of from 0.05 to 6.0.
 7. Theprocess of claim 1, wherein the first solution comprises vanadium andphosphorus at a molar ratio of vanadium to phosphorus of from 0.1 to4.0.
 8. The process of claim 1, wherein the alumina catalyst supportmaterial is in the form of particles having a size from 10 μm to 200 μm.9. The process of claim 1, wherein the alumina catalyst support materialis in the form of particles having an average particle size from 60 μmto 100 μm.
 10. The process of claim 1, wherein the alumina catalystsupport material comprises alumina having a BET pore volume from 0.4cc/g to 1.0 cc/g.
 11. The process of claim 1, wherein the secondsolution has a concentration of the active cobalt catalyst componentsuch that the catalyst precursor obtained comprises from 5 wt % to 45 wt% cobalt.
 12. The process of claim 1, wherein the second solution has aconcentration of the active cobalt catalyst component such that thecatalyst precursor obtained comprises from 20 wt % to 35 wt % cobalt.13. The process of claim 1, where in the ratio of glutaric acid in thesecond solution to the modified support surface area is from 2 to 15μmol glutaric acid/m² of modified support surface area.
 14. The processof claim 1, wherein the catalyst precursor further comprises a promoterselected from the group consisting of platinum, ruthenium, silver,palladium, lanthanum, cerium and combinations thereof.
 15. The processof claim 14, wherein the promoter comprises from 0.01 wt % to 5 wt %.16. A process for preparing a Fischer Tropsch catalyst, the processcomprising: a. preparing a catalyst precursor according to claim 1; andb. reducing the catalyst precursor to activate the catalyst precursor toobtain the Fischer Tropsch catalyst.